Energy-Efficient Envelope Design for Apartment Blocks—Case Study of A Residential Building in Spain

Round 1

Reviewer 1 Report

The paper presents an algorithmic approach aiming to define the optimum insulation thickness for multi-apartment building blocks with different energy demand per apartment. It is a first attempt to use an optimization approach to solve the well-known problem of varying energy demand per apartment in multi-apartment buildings.

The work claims trying to answer two questions:

• “when proposing a measure to reduce the energy needs of a building based on increasing the insulation of the facade, why propose the same level of insulation for the entire apartment block? The proposal should be different from one dwelling to another depending on their individual characteristics.
• Why are the heating and cooling needs in an apartment block very different from one flat to another?

However, the work presented is too limited to be able to answer such key questions and the conclusions of the paper do not address them.

The major weakness of the work is its core assumption that in order to account for the energy demand of each apartment comprising a multi-storey residential building it is appropriate to optimize the passive - envelop energy reduction measures hence avoid oversizing of insulation thickness and window thermal characteristics. This assumption does not take into account aesthetic-architectural and fire safety requirements which must be uniform for the entire building and cannot be individualized per apartment or facade.

Additionally, the analysis does not consider:

• cost-benefit aspects (insulation thickness does not strongly affect its cost, whereas the costs for creating an aesthetically uniform result might be higher),
• manufacturing limitations (e.g. insulation materials are produced in standard dimensions and non-standard production would increase their cost)
• compliance with national regulations and codes (generally energy classifications cover a range of values and refer to the entire building not apartment)
• the role of active systems in covering the demand differences per apartment.

The authors quote that the different apartments of the block have significantly different energy demands without quantifying how much of this difference is associated with identified different parameters (e.g. orientation, window to wall ratio, shading, user profile). A systematic analysis and quantification of the parameters that may affect these differences is missing as well as literature data and previous studies,

The introduction generally mentions passive and active measures to reduce energy consumption in buildings and does not review and reference relevant passive measure optimization approaches.

The “bootstrap resampling technique” should be explained more in detail and references should be added.

It is not clear how the energy demand of each apartment was calculated with the HULC software.

The analysis on the cooling demands, which is quite important due to the geographic location of the demonstration building is very brief and not  

The paper does not describe adequately the proposed final solution in terms of window interventions.

Overall, the approach is at its first steps. It requires further elaboration and analysis to formulate a more realistic approach. The paper must be thoroughly revised to address the above comments.

Author Response

Dear Reviewer,

The authors of the article would like to thank you for the thorough review you have made thanks to which we hope to have improved it.

In the accompanying document we respond to all of your comments.

Thank you very much.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear author,

Please consider the following remarks.

1. The preliminary remark is as follows. The reviewer analyzes this manuscript as a research article, but not as a technical report on RECO2ST project.

2. The title of the article includes the word Cádiz, which is unfamiliar to most readers. The title contains the term "apartments blocks", this term is no longer found in the article.

3. The Abstract does not contain brief formulations of the new scientific results obtained by the author. The Abstract refers to Europe and the Old Continent, which immediately reduces readers' interest from other regions (Line 19).

4. The literature review is unsatisfactory. The list of reference includes mainly Internet resources, regulatory and manual documents. Despite the huge number of publications in this research field, there are very few research publications in the list of references.

The list of references for the last five years includes only:

• One article for 2020 [20].
• One book and one article for 2018 [7], [15].
• One article for 2017 [14].
• One article for 2016 [12].

Thus, the research is not properly motivated in the INTRODUCTION section by analyzing contemporary publications in leading international journals.

5. The object of research, the study's goal and objectives are not clearly defined in the INTRODUCTION section.

6. It is not clear if the author presents methodology (Line 26), or shows a methodology (Lines 108, 110, 368), or proposes it (Line 30, 224.297, 329).

The author does not define the word "methodology," which is so often used in the article. Moreover, the section "2. Methodology" itself begins with the subsection "2.1. Optimum solution search method".

This mixture of "methodology" and "method" completely confuses readers and makes it impossible to understand what is "methodology" means. It is not clear whether the "methodology" is identical with the "optimization method" (Lines 377, 381, 383) or the "optimal solution search method" (Lines 113, 205).

The text "This method enables different design parameters to be combined simultaneously with many input values" is incomprehensible (Line 158). It is not clear what "this" is. That piece of text appears in the middle of a subsection. It is not clear what the rest of the text refers to. Whether the following text is a continuation of this method's description, or the following text describes another method, or describes the "methodology" indicated in the section's title.

It is unclear when and by whom the method was proposed, whether the method was proposed in this article or previously published articles [8,9] (Line 61).

On line 377, the method is called "The optimization method," in contrast to the previously mentioned "optimum solution search method."

7. The author writes that "More details about the calculation method can be consulted in [26]" (Lines 218, 219). But when you follow the link [26], the message "La página solicitada/publicaciones/condiciones-de-aceptacion-de-procedural-imientos-alternativos-lider-y-457 no se ha podido encontrar" appears. This means that the requested page could not be found.

8. There is no comparison with the results of other researchers in the RESULTS and DISCUSSION section.

9. The author named the article as a Case Study. But the article looks more as a technical report than as a study. There is no scientific generalization of the obtained particular results. No conclusions have been drawn about the possibility of transferring the obtained partial results to other similar buildings. The manuscript is actually an engineering calculation of the thickness of thermal insulation, not a scientific study.

10. The CONCLUSIONS section does not include brief interpretations of new scientific results. The results obtained in the study would be of little interest to the international scientific community.

11. The level of consideration by the author of the problem of increasing energy efficiency is low. It is at the level of optimization of the U-values ​​of the building envelope. This level of consideration corresponds to the end of the last century and the beginning of this century. The author completely ignored modern approaches to energy conservation, such as:

• Double skin façades,
• Phase change materials,
• Aerogel-enhanced systems (including aerogel blankets),
• Innovative foams,
• Retroreflective materials,
• Climate-sensitive materials,
• And so on, and so on.

Here the reviewer lists the publications of only one author as an example of modern approaches:

• Berardi, U. Overview of recent researches in IAQ, ventilation, and energy conservation. Build. Simul. 2020, 13, 977–978, doi:10.1007/s12273-020-0716-0.
• Wi, S.; Berardi, U.; Loreto, S.D.; Kim, S. Microstructure and thermal characterization of aerogel–graphite polyurethane spray-foam composite for high efficiency thermal energy utilization. J. Hazard. Mater. 2020, 397, doi:10.1016/j.jhazmat.2020.122656.
• Berardi, U.; Nikafkar, M.; Wi, S.; Kim, S. Experimental verification of the theoretical aging of vacuum insulated panels. J. Ind. Eng. Chem. 2020, 90, 300–304, doi:10.1016/j.jiec.2020.07.027.
• Berardi, U.; Kisilewicz, T.; Kim, S.; Lechowska, A.; Paulos, J.; Schnotale, J. Experimental and numerical investigation of the thermal transmittance of PVC window frames with silica aerogel. J. Build. Eng. 2020, 32, doi:10.1016/j.jobe.2020.101665.

Author Response

Dear Reviewer,

The authors of the article would like to thank you for the thorough review you have made thanks to which we hope to have improved it.

In the accompanying document we respond to all of your comments.

Thank you very much.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Dear authors,

The article has been significantly improved and can be published in its present form, after minor English improvements. Please, take care to define all acronyms.

Author Response

Again and first of all, the authors would like to thank the reviewer for the effort made in reviewing the article as well as his/her comments and suggestions that will help improve it.

We send attached a document answering the comments.

Thank you very much

Author Response File: Author Response.docx

Reviewer 2 Report

Dear author, thank you for the changes and additions made to the article. The number of my comments has decreased significantly.
1. The following phrase in lines 398-399 is not clear: "In addition, excessive unnecessary insulation is more expensive and can lead to an increased risk of overheating in summer."
First of all, it is not clear what excessive insulation can lead to overheating or the risk of overheating. If the author uses the word "risk", then it is necessary to give in the article at least a qualitative risk assessment, apply the theory of risk, etc.
Further, the keyword in this phrase is "summer". In the Spanish summer conditions, it is not necessary to heat, but to cool the air in living spaces. And the thicker the thermal insulation layer, the lower the energy consumption for air cooling. "Unnecessary" thermal insulation can not lead to overheating in the summer, rather the opposite.
2. The author did not react in any way to comment number 11 of the reviewer. Apparently, the reason is that the reviewer did not clearly express his approach. There are many relatively new ways to improve the energy efficiency of a residential building:
• Double-walled facades,
• Phase transition materials,
• Systems with added airgel (including airgel blankets),
• Innovative foams,
• Reflective materials,
• Climate sensitive materials.
The author limits himself to optimizing only the U-value, which is not explained in the article's main text and the CONCLUSION. Such explanations, in the opinion of the reviewer, are necessary.
3. The author's statement in lines 401-403 is substituted as an erroneous one:
"In addition, in order not to affect the energy efficiency of the building in summer, new insulation should be placed on the outer layer of the outer walls and roof, thus ensuring the thermal inertia of the building." The thermal inertia of a building determines by materials with a high thermal capacity. These materials are concrete, bricks, and others. The thermal inertia of a building can be increased with phase change materials. Thermal insulating materials have low thermal conductivity, and at the same time, extremely low heat absorption capacity. Thermal insulating materials can influence a building's temperature and cannot significantly change the building's thermal inertia.
4. At line 405, the research object is identified as "a five-story apartment building." In contrast to this, the article's title indicates "residential building" as an object of research. The consistency of terminology should be ensured.

Author Response

Again and first of all, the authors would like to thank the reviewer for the effort made in reviewing the article as well as his/her comments and suggestions that will help improve it.

We send attached a document answering all comments.

Thank you very much

Author Response File: Author Response.docx